An efficient, short synthesis of the antitumor agent AT 125 (5-isoxazoleacetic acid, a-amino-3 chloro-4,5,-dihydro) is proposed. Further work will involve adapting the synthesis to potentially active derivatives. A key step to the overall route is the formation of the isoxazoline ring. This will be accomplished by cycloadding benzenesulfonylnitrile oxide to an N-protected vinyl glycine derivative. Stereochemical control of the cycloaddition reaction will be achieved by biasing attack of the nitrile oxide to one face of the dipolarophile through careful selection of associative and steric factors. In particular, metal-ion association of the dipolarophile carboxylate group and nitrile oxide oxygen should dictate the desired stereochemical outcome. The cycloadduct will then be transformed in a short series of steps to AT-125. Substitution reactions of this compound will permit the preparation of a number of potentially active derivatives. Carrying out the key cycloaddition reaction with other beta, mu-unsaturated-alpha-amino acids will permit the preparation of additional derivatives.